The present invention relates to techniques for effective use in semiconductor integrated circuit devices having an on-chip voltage controlled oscillator (VCO) and a phase-locked loop (PLL) circuit which includes the VCO within its loop. More particularly but not exclusively, the invention relates to techniques for effective use in semiconductor integrated circuit devices for the communication use employing offset PLL architectures and having a built-in signal transmission VCO for up-converting the frequency of a transmission signal and a built-in PLL circuit including the VCO within its loop in a wireless communication system such as for example portable or “mobile” telephone, and also relates to wireless communication systems.
In wireless communication systems such as mobile or cellular phones, semiconductor integrated circuit devices for the communication use (referred to as high-frequency ICs hereinafter) are used which synthesize a local oscillation signal of high frequency to a receiving signal and/or a sending signal to thereby perform down-conversion and up-conversion, and which perform modulation of the send signal along with demodulation of the receive signal. In such high-frequency ICs, there is the so-called offset PLL architecture for applying quadrature modulation to transmission I, Q signals using a carrier wave of intermediate frequency, and also for mixing together a feedback signal from the output side of a signal transmission VCO and a high-frequency oscillation signal from RFVCO to thereby effectuate down conversion into an intermediate frequency signal equivalent to a frequency difference (offset), and thereafter performing phase comparison of this signal with a signal obtained after the above-noted quadrature modulation to thereby control the transmission VCO in accordance with a phase difference thus detected.